The present invention relates to automotive transmissions and more particularly to synchronizer clutches for controlling changes in transmission gearing.
Synchronizer clutch assemblies are used to facilitate the smooth engagement of meshing teeth during changes of gears in a transmission. A typical assembly includes a hub positioned between two gears of different pitch diameter, the hub having a central opening in which are formed a plurality of teeth for drivingly mounting the hub on a drive shaft. A clutch sleeve with internal clutch teeth is mounted for axial sliding movement on the hub, and each gear also carries corresponding external sleeve teeth which are engageable by the inner teeth of the sleeve in order to create a drive path from the shaft, through the hub and sleeve to the gear. Each gear also carries an external cone clutch surface which is engageable by a complementary internal cone clutch surface formed on a synchronizer ring disposed between the hub and each gear. Upon movement of the sleeve towards a gear, the associated synchronizer rings are first engaged and caused to move axially towards the gear so as to bring its internal cone surface into engagement with the external surface formed on the gear. The resulting frictional engagement ensures that the speeds of the hub and gear are synchronized before the sleeve is slide further into engagement with the sleeve teeth of the gear, thereby ensuring smooth engagement. Examples of such synchronizers are shown in European Patent no. 0756098, U.S. Pat. No. 2,221,900 and U.S. Pat. No. 3,366,208.
These conventional synchronizers have the disadvantage, however, that if the cone surfaces on the gear and the synchronizer ring are formed with taper angles that are too small, that is, which are shallower than the friction angles determined by the material dependent frictional μ factors, then cone jam occurs, in which the frictional forces between the synchronizer ring and the gear are so great as to prevent disengagement of the two parts and hence jam the transmission in gear.